PhD Admission with an Imperial 2:1

So I just finished my third year of the 4 year MSci Physics with Theoretical Physics course at Imperial College and am currently on an average score of 68%. Now I really feel like it'll go down to the wire with regards to whether I get a first or not, especially as they've now (this year, for my year, thanks a bunch) removed all vivas. I was wondering if I was to get a high 2:1 (talking 68% and upwards and quite a few of my exams with firsts) but not quite get over that 70% mark whether I would then be unable to pursue a PhD in one of the other good UK universities (Oxford, Cambridge, Durham etc) or whether it will significantly affect my chances of success when applying there? They scale like hell in my university so that only the very top can get over 70%, it's really frustrating.